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Chikungunya virus (CHIKV) is becoming a global concern due to the increasing number of outbreaks throughout the world and the absence of any CHIKV-specific vaccine or treatment. Virus-like particles (VLPs) are multistructured proteins that mimic the organization and conformation of native viruses but lack the viral genome. They are noninfectious and potentially safer vaccine candidates. Recent studies demonstrated that the yield of CHIKV VLPs varies depending on the strains, despite the 95% amino acid similarity of the strains. This might be due to the codon usage, since protein expression is differently controlled by different organisms. We optimized the region encoding CHIKV structural proteins, C-E3-E2-6k-E1, inserted it into a mammalian expression vector, and used the resulting construct to transfect 293 cells. We detected 50-kDa proteins corresponding to E1 and/or E2 in the cell lysate and the supernatant. Transmission electron microscopy revealed spherical particles with a 50- to 60-nm diameter in the supernatant that resembled the native CHIKV virions. The buoyant density of the VLPs was 1.23 g/mL, and the yield was 20 µg purified VLPs per 108 cells. The VLPs aggregated when mixed with convalescent sera from chikungunya patients, indicating that their antigenicity is similar to that of native CHIKV. Antibodies elicited with the VLPs were capable of detecting native CHIKV, demonstrating that the VLPs retain immunogenicity similar to that of the native virion. These results indicated that CHIKV VLPs are morphologically, antigenically, and immunologically similar to the native CHIKV, suggesting that they have potential for use in chikungunya vaccines.

Objectives: Chikungunya virus (CHIKV) is an alphavirus belonging to the Togaviridae family. Alphaviruses cause a chronic non-cytopathic infection in mosquito cells, while they develop a highly cytopathic infection in cells originating from various vertebrates. In this study, we compared the cytopathic effect (CPE) induced by CHIKV in Vero cells and a mosquito cell line, C6/36 cells., Methods: CPE and the virus titers were compared between the CHIKV-infected C6/36 and Vero cells. Apoptosis was measured by TUNEL assay, and the differences between the C6/36 and Vero cells were compared., Results: CHIKV infection induced strong CPE and apoptosis in the Vero cells, but light CPE in the C6/36 cells. The virus titers produced in the C6/36 cells were much higher than those produced in the Vero cells., Conclusions: The reason CHIKV induced strong CPE is that this virus triggers strong apoptosis in Vero cells compared with C6/36 cells. CHIKV established a persistent infection in C6/36 cells after being passaged 20 times. CHIKV infection in mosquito cells was distinct from that in Vero cells. The cell and species specificity of CHIKV-induced cell death implies that the cellular and viral regulators involved in apoptosis may play an important role in determining the outcome of CHIKV infection., (Copyright © 2012 S. Karger AG, Basel.)

Background: Double-stranded RNA (dsRNA) and its mimic, polyinosinic acid: polycytidylic acid [Poly (I:C)], are recognized by toll-like receptor 3 (TLR3) and induce interferon (IFN)-β in many cell types. Poly (I:C) is the most potent IFN inducer. In in vivo mouse studies, intraperitoneal injection of Poly (I:C) elicited IFN-α/β production and natural killer (NK) cells activation. The TLR3 pathway is suggested to contribute to innate immune responses against many viruses, including influenza virus, respiratory syncytial virus, herpes simplex virus 2, and murine cytomegalovirus. In Chikungunya virus (CHIKV) infection, the viruses are cleared within 7-10 days postinfection before adaptive immune responses emerge. The innate immune response is important for CHIKV clearance., Results: The effects of Poly (I:C) on the replication of CHIKV in human bronchial epithelial cells, BEAS-2B, were studied. Poly (I:C) suppressed cytopathic effects (CPE) induced by CHIKV infection in BEAS-2B cells in the presence of Poly (I:C) and inhibited the replication of CHIKV in the cells. The virus titers of Poly (I:C)-treated cells were much lower compared with those of untreated cells. CHIKV infection and Poly (I:C) treatment of BEAS-2B cells induced the production of IFN-β and increased the expression of anti-viral genes, including IFN-α, IFN-β, MxA, and OAS. Both Poly (I:C) and CHIKV infection upregulate the expression of TLR3 in BEAS-2B cells., Conclusions: CHIKV is sensitive to innate immune response induced by Poly (I:C). The inhibition of CHIKV replication by Poly (I:C) may be through the induction of TLR3, which triggers the production of IFNs and other anti-viral genes. The innate immune response is important to clear CHIKV in infected cells.

Objectives: Chikungunya virus (CHIKV) is an alphavirus belonging to the Togaviridae family. Alphaviruses cause a chronic non-cytopathic infection in mosquito cells, while they develop a highly cytopathic infection in cells originating from various vertebrates. In this study, we compared the cytopathic effect (CPE) induced by CHIKV in Vero cells and a mosquito cell line, C6/36 cells. Methods: CPE and the virus titers were compared between the CHIKV-infected C6/36 and Vero cells. Apoptosis was measured by TUNEL assay, and the differences between the C6/36 and Vero cells were compared. Results: CHIKV infection induced strong CPE and apoptosis in the Vero cells, but light CPE in the C6/36 cells. The virus titers produced in the C6/36 cells were much higher than those produced in the Vero cells. Conclusions: The reason CHIKV induced strong CPE is that this virus triggers strong apoptosis in Vero cells compared with C6/36 cells. CHIKV established a persistent infection in C6/36 cells after being passaged 20 times. CHIKV infection in mosquito cells was distinct from that in Vero cells. The cell and species specificity of CHIKV-induced cell death implies that the cellular and viral regulators involved in apoptosis may play an important role in determining the outcome of CHIKV infection. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]